its the claw size. We have two 60 pound Bassett Hounds and we have one room in hardwood flooring. I keep my dogs nails cut regularly and they present no problem, but when they get long, that's another story.
I would imagine that even a small dog could do scratching damage when the nails get out of hand and start to curl downward.
Beware, manicuring nails of dogs can be serious if you don't know what your doing.